The invention relates to a rotary scanning device having a stationary guide drum around which a magnetic tape is wrapped along a helical path, and a cylindrical insert mounted in a radial bore in the guide drum, which insert has one end face adapted to the surface of the guide drum and carriers a magnetic head for scanning a servo track in a slot in the end face.
When signals are recorded on a magnetic tape, which is wrapped around a rotary scanning device along a helical path, a plurality of track portions are recorded which are inclined relative to the direction of movement of the magnetic tape. Generally, a tracking signal is recorded in a longitudinal track of the magnetic tape, the so-called servo track, in order to ensure that in a reproduction mode the magnetic heads can follow the previously recorded tracks, the pulses of said tracking signal being in a fixed relationship to the transverse or inclined track portions on the magnetic tape. In a recording mode the tracking signal is recorded in the servo track by means of a separate stationary servo head and in a reproduction mode it is subsequently read from the servo track.
Magnetic tapes are subjected to several influences affecting the mechanical dimensions of the magnetic tape. Such influences are, for example, changes of the atmospheric humidity, temperature variations, and also mechanical loads. Therefore, it has proved to be effective to arrange the servo head at a location which, viewed in the tape transport direction, is spaced at a fixed distance from the location where the signals are recorded and reproduced. If this is not the case the recorded oblique tracks will not be scanned correctly by the magnetic reproducing heads, resulting in a degradation of the signal-to-noise ratio of the reproduction signal.
In order to avoid these problems the geometrical position of scanning of the recorded signals and that of the tracking signals are arranged as close as possible to one another in the longitudinal direction of the magnetic tape. This step enables the influence of errors caused by a length variation of the magnetic tape to be reduced.
DE 25 22 583 A1 discloses a device for securing a magnetic servo head in the stationary guide drum of a helical-scan magnetic-tape apparatus. The guide drum has a radial bore for receiving a cylindrical insert having one end face adapted to the cylindrical surface of the guide drum and carrying the magnetic servo head in a slot in the end face.
For the mechanical adjustment of the track position, during which the distance between the oblique tracks and the tracking pulses in the servo track is to be adjusted, it is customary that the rotary body which carries the magnetic heads for scanning the oblique tracks at its periphery is moved in its axial direction. This is effected via a drive shaft of the rotary body. However, tolerances of the bearing element fits then give rise to tilting of the drive shaft. This gives rise to track curvatures in the scanning direction, which complicate a compatible reproduction of the signals recorded in the oblique tracks.